Arrangement for line-testing

ABSTRACT

This invention generally relates to the arrangements for testing subscriber loops. The invention is based on a solution wherein a test head is behind the high-pass filter of the splitter. In order that this solution is possible, the splitter, i.e. the splitter box has to contain a relay and a relay control element. When a subscriber line is to be tested the test head sends a DC pulse to the relay control element, which directs the relay to connect the subscriber loop to bypass wirings through which the test head can perform necessary testing measurements. When the testing is over the relay control element directs the relay to switch back for connecting the subscriber loop to the common port of the filters.

FIELD OF THE INVENTION

[0001] This invention generally relates to the arrangements for testingsubscriber loops, and more particularly to the arrangements, whichcomprise a splitter for separating low and high frequency traffic.

BACKGROUND OF THE INVENTION

[0002]FIG. 1 shows an example of a known subscriber line testingarrangement, wherein the subscriber line (1A) carries both normal POTSor ISDN traffic and xDSL (such as ADSL or VDSL) traffic. The arrangementaccording to FIG. 1 needs a splitter (3) for separating the POTS/ISDNtraffic and the xDSL traffic. POTS (Plain Old Telephone Service) andISDN (Integrated Services Digital Network) traffic are transmitted in alow frequency range while the xDSL (some Digital Subscriber Line system)traffic is transmitted in a higher frequency range. The splitter isnormally a high-pass/low-pass filter, which comprises a common port (3A)for a subscriber loop, a low-pass port 3B) for a POTS/ISDN device (4),and a high-pass port (3C) for an xDSL device (5). The POTS/ISDN and XDSLdevices have connections to a network.

[0003] In order for the line testing of the subscriber loop (1A) to bepossible, a line tester (2) must be situated in front of the splitterbefore the subscriber loop from the subscriber (1) reaches the splitter,i.e. the subscriber loop is connected to the splitter through the linetester. This is due to the fact that it is impossible to measure alldesired parameters through the splitter, i.e. through the high-pass orlow-pass filter. It is worth noting that at subscriber's premise theloop is connected to a terminal, which also comprises a splitter.

[0004]FIG. 2 shows an example of how wiring is performed in a realimplementation. Subscriber loops from subscribers (1) are connected to aMDF (Main Distribution Frame) (6), from where the subscriber loops areconnected forward to the line tester (2). In the line tester thesubscriber loop, which is to be tested, is connected to a test line (2D)(pair line) using a subscriber line dedicated relay (2C). A test head(2A), which is connected to the test line, performs line testingmeasurements. If the subscriber loop does not need to be tested therelay connects the subscriber loop back to the, MDF.

[0005] After the line tester the subscriber loop is connected from theMDF (6) to a subscriber loop dedicated splitter, more particularly intothe common port (3A) of the splitter. In the splitter, the subscriberloop branches to two separate lines: a line of low frequency range and aline of high frequency range. Both lines, the line of low frequencyrange from the low-pass port (3B) and the line of high frequency rangefrom the high-pass port (3C), are wired to the MDF from where they areconnected to a POTS/ISDN device (4) and an xDSL device (5).

[0006] As can be noticed, the MDF connects all devices together. Thusthe wiring can be multiple and when implementing it is easy to makemistakes. For helping the observing of FIG. 2 the wirings have beenmarked in different lines. Each device requires wiring space in the MDF,so the more devices concerning a dedicated subscriber loop are neededthe less subscriber loops are possible to be connected to the MDF. Itshould be also noted that a line tester can handle several subscriberloops and in spite of what is illustrated in FIG. 2 the POTS/ISDNdevices (4) can be one unit, which can handle several subscriber loopsas well as xDSL devices (5).

[0007] The intention of the invention is to eliminate these drawbackswhen making it possible to perform line testing through a splitter.Furthermore, since the splitter is a passive element it is desired tokeep it passive in an arrangement according to the invention as well.The aims of the invention are achieved in a way described in the claims.

SUMMARY OF THE INVENTION

[0008] The invention is based on a solution wherein a test head isbehind the high-pass filter of the splitter. In order that this solutionis possible, the splitter, i.e. the splitter box has to contain a relayand a relay control element. The relay makes it possible to bypass thehigh-pass filter during the testing of the subscriber loop. When asubscriber line is to be tested the test head sends a DC pulse to therelay control element, which directs the relay to connect the subscriberloop to bypass wirings through which the test head can perform necessarytesting measurements. When the testing is over the relay control elementdirects the relay to switch back for connecting the subscriber loop tothe common port of the filters.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] In the following the invention is described in more detail bymeans of FIGS. 1-7 in the attached drawings where.

[0010]FIG. 1 illustrates an example of a present arrangement for testinga subscriber loop,

[0011]FIG. 2 illustrates an example of wirings in a presentimplementation,

[0012]FIG. 3 illustrates an example of an arrangement according to theinvention,

[0013]FIG. 4 illustrates an example of an xDSL device with line testingequipment,

[0014]FIG. 5 illustrates an example of a line card wherein line testingequipment is combined,

[0015]FIG. 6 illustrates another example of a line card wherein linetesting equipment is combined, and

[0016]FIG. 7 illustrates a flow chart describing an embodiment of themethod according to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017]FIG. 3 shows an example of an arrangement according to theinvention. When the subscriber loop is to be tested a DC pulse is sentfrom a test head to the relay control element (32). in the splitter box(3). The test head can be situated in the XDSL device (5) or in anothersuitable place. However, the DC pulse is transmitted to the splitter boxthrough the high-pass lines (35). The relay control element is connectedto the high-pass line through control wires (34). Since the high-passfilter forms an open circuit for DC current the pulse does not propagatethrough the high-pass port (3C).

[0018] The relay control element (32) has a suitable integration time ofthe DC pulse before it can direct the relay (31) to switch for making aconnection to the bypass wires (33). The other ends of the bypass wiresare connected to the high-pass line (35). The bypass wires make itpossible for the test head to perform the test measurements desired. Therelay control element forms a high impedance towards the xDSL device sothe relay control element does not disturb the line testingmeasurements. DC power is not fed into the high-pass line during themeasurements when the relay (and the arrangement) is in a line testingstate.

[0019] After the line testing measurements have been made and thearrangement (and the relay) is to be returned to the normal state, therelay control element directs the relay to switch back for breaking thebypass connection and for connecting the subscriber loop to the commonport (3A) of the filters of the splitter. There are at least twopossibilities to create a command for switching the relay back to theposition of the normal state (connecting the subscriber loop to thecommon port of the filters of the splitter): 1) the relay controlelement has a function for time-out after which the relay controlelement directs the relay, or 2) the test head inserts an oppositepolarity DC pulse to the relay control element, which as a response forthis pulse directs the relay.

[0020] The relay control element and the relay are splitter dedicated,assigned to one subscriber. Since the relay and the relay controlelements are passive it is possible to maintain the splitter box assimply as possible. However, it is worth noting that in some cases itcan be useful if the relay control element (and maybe the relay as well)is an active element, i.e. it needs it's own power feeding system fromoutside.

[0021]FIG. 4 shows an example of an xDSL device (5) with line testingequipment The XDSL device can be, for example, a DSLAM (DigitalSubscriber Line Access Multiplexer). The DSLAM contains a number of linecards (44). Before the high-pass lines from the splitters are wired tothe line cards, the lines are connected to relays (42) through which itis possible to connect the high-pass lines (i.e. the subscriber lines)to the test line (43) which in turn is connected to the test head (41).The test head does not have to be in the DSLAM but it can be in anysuitable place. However, it is required that a connection can be set upfrom the test head to the subscriber loop to be tested.

[0022] It is also possible to combine a test head into the line card.FIG. 5 shows an example of this kind of arrangement The test head (51)is situated in front of an AFE (Analog Front End) (52) from the view ofthe high-pass line (the subscriber line). The test head block containsequipment for connecting the test head to the line to be measured. TheAFE contains line drivers (53, 54) for the incoming traffic and theoutgoing traffic, an ADC (Analog to Digital Converter) (55) for incomingtraffic, a DAC (Digital to Analog Converter) (56) for outgoing traffic,and a receiver (57) for doing certain functions. A DSP (Digital SignalProcessor) (58) controls the operation of the AFE and performs certaintasks for the transmission traffic. It can be possible that the DSP andthe receiver are combined.

[0023]FIG. 6 shows another example of how a test head is combined into aline card. In this case the AFE block contains the test head. Thefunctionality of the line card according to FIG. 6 is the same as thefunctionality of the line card according to FIG. 5.

[0024]FIG. 7 shows a flow chart describing an embodiment of the methodaccording to the invention. When a subscriber line is to be tested a DCpulse is sent (71) to the relay control element in the splitter boxthrough the line (high-pass line) connecting an xDSL device and thesplitter box. As a response to the DC pulse the relay control elementdirects, i.e. commands, the relay to switch into another position formaking (72) a bypass connection between the subscriber loop and the testhead. The test head performs (73) the testing measurements through thebypass connection. After the measurements, the relay is commanded by therelay control element to switch (74) back to the normal state, i.e. tomake connection between the filters of the splitter and the subscriberloop and to break the bypass connection.

[0025] So, the invention makes it possible to perform line testingmeasurements behind a splitter. Wiring in an access site, i.e. the placewhere the splitter is, is simple, and the splitter remains passive. Thetest head can be situated in any suitable location.

[0026] It is worth noting that the invention can be realized in otherways than those described above. For example, the test head can besituated behind the low-pass line (FIG. 3, 36) in which case the testhead could be in the POTS/ISDN device (FIG. 3, 4). However, now, thepulse, which is needed to give a command for starting the line testing,can not be a DC pulse (notice that the relay control element isconnected to the low-pass line in this case) since the DC pulse willpropagate to the subscriber line through the low-pass filter. Due tothis, the pulse should be a high-frequency signal. However, thissolution is more difficult to perform and the relay control elementshould preferably be an active element, which is not desirable.

[0027] Taking all above-mentioned matters into account, it is evidentthat the invention can be implemented in many ways, in the scope of theinventive idea.

1. An arrangement for testing a subscriber line comprising a splitter,characterized in that the arrangement comprises: a test head, situatedbeyond the splitter from the view of the subscriber line, and connectedto a filter port of the splitter, a relay, situated in front of a commonport of filters of the splitter from the view of the subscriber line,and connected to the subscriber line and the common port of the filtersof the splitter, for making a connection between the common port of thefilters and the subscriber line in a normal state, bypass wires betweenthe filter port of the splitter and the relay, making it possible forthe relay to connect the test head to the subscriber line through thefilter port of the splitter in a line testing state, a relay controlelement connected to the filter port of the splitter and the relay forcontrolling switching actions of the relay in response to commandscoming from the test head.
 2. An arrangement according to claim 1,characterized in that the relay, bypass wires, and the relay controlelement are located in a box wherein the splitter has been implemented.3. Am arrangement according to claim 1 or 2, characterized in that thefilter port of the splitter whereto the test head is connected is ahigh-pass port.
 4. An arrangement according to claim 3, characterized inthat the test head and elements needed to connect the test head to aline coming from the filter port of the splitter, are situated in anxDSL device.
 5. An arrangement according to claim 4, characterized inthat the test head is situated in front of a line card from the view ofthe line coming from the filter port.
 6. An arrangement according toclaim 3 or 4, characterized in that the command from the test head forconnecting the arrangement to the line testing state is a DC pulse. 7.An arrangement according to claim 6, characterized in that the commandfrom the test head for connecting the arrangement to the normal state isDC pulse of opposite polarity to the DC pulse used for connecting thetest head in the line testing state.
 8. An arrangement according toclaim 6, characterized in that the relay control element comprises meansfor creating a command for connecting the arrangement to the normalstate.
 9. An arrangement according to claim 4, characterized in that thetest head is combined with a line card, which is dedicated to thesubscriber line.
 10. An arrangement according to claim 1 or 2,characterized in that the filter port whereto the test head is connectedis a low-pass port.
 11. An arrangement according to claim 10,characterized in that the test head and necessary elements, which areneeded to connect the test head to a line coming from the filter port,are situated in an POTS/ISDN device.
 12. An arrangement according toclaim 11, characterized in that the test head is situated in front of aline card from the view of the line coming from the filter port.
 13. Anarrangement according to claim 10 or 11, characterized in that thecommand from the test head for connecting the arrangement to the linetesting state is a high-frequency signal.
 14. An arrangement accordingto claim 13, characterized in that the command from the test head forconnecting the arrangement to the normal state is another high-frequencysignal.
 15. An arrangement according to claim 13 or 14, characterized inthat the relay control element comprises means for creating a commandfor connecting the arrangement to the normal state.
 16. A method fortesting a subscriber line, the method comprising the steps of: sending acommand from a test head to a relay control element, directing a relayto switch to a line testing state as a response to the command receivedby the relay control element, switching the relay for making a bypassconnection that passes a splitter, performing testing measurements, andswitching the relay for breaking the bypass connection that passes thesplitter and for returning to a normal state.
 17. A method according toclaim 16, the method further comprising the step of sending a commandfrom the test head to the relay control element directing a relay forswitching to the normal state and for breaking the bypass connection.